The present invention relates to ceramic materials, and in particular to multi-component ceramic composite materials.
Oxide ceramics such as alumina (Al2O3), zirconia (ZrO2), titania (TiO2), chromia (Cr2O3), silica (SiO2), and yttria (Y2O3) have been widely used as coating materials to improve the surface properties of bulk materials. They are especially useful in applications where both wear and corrosion resistance is required. For example, alumina/titania ceramic coatings have excellent wear, erosion, fretting and cavitation resistance; heat resistance up to 540xc2x0 C.; excellent resistance to most acids and alkalis; resistance to wetting by common aqueous solutions, and high dielectric strength. Because of the many advantageous properties of ceramic oxide coatings, particularly those prepared by thermal spray, they have found broad utility in a number of demanding technical applications, such as repairing steam valve stems, in land based gas turbines, diesel engines, cutting tools, medical implants, and catalytic converters.
A wide variety of multi-component ceramic oxides based on alumina as the major component have been reported, including a number suitable for use in thermal spray applications. For example, U.S. Pat. No. 4,141,743 discloses a composite powder suitable for use in thermal spray applications as a wear and/or corrosion resistant coating consisting of chromic oxide, magnesium oxide, iron oxide, titanium oxide, and aluminum oxide. U.S. Pat. No. 3,802,893 discloses a polycrystalline abrasion-resistant alumina composition having aluminum oxide, magnesium oxide, and samarium oxide. U.S. Pat. Nos. 4,881,951, 5,651,801 and 5,669,941 disclose abrasive grits formed of oxides of aluminum and rare earth metals. U.S. Pat. No. 5,498,269 discloses a ceramic abrasive comprising alumina, zirconia, and very small amounts of rare earth oxides. U.S. Pat. No. 5,059,095 discloses turbine rotor blade tips coated with alumina-zirconia ceramics.
Rare earth ceria has been used as an additive to alumina coatings formed by thermal spray processes, where it functions to refine the coating microstructure and decrease coating porosity. Ceria has also been used to aid the formation of fine net-shaped micro cracks in plasma sprayed alumina coatings, which could release the coating stress, resulting in an improved thermal shock resistance of the coating.
Zirconia or partially stabilized zirconia in thermal barrier coating systems is disclosed in U.S. Pat. Nos. 5,498,484 and 5,530,050. Zirconia powders containing ceria and yttria are disclosed in U.S. Pat. No. 5,530,050.
Additionally, ceria added to YSZ (yttria-stabilized zirconia) coatings can improve thermal cycling behavior. Ceria may also be added to stabilize zirconia for use as powder feedstock in plasma sprayed thermal barrier coatings. Ceria may also be added to a zirconia solution to prepare mixed oxides of ceria-zirconia, or to alumina-zirconia to produce processed powders for thermal spray applications.
Zirconia or YSZ has been used as an additive in certain metal ceramic thermal spray of nanostructured feedstocks. Such zirconia additives improve the material""s thermal impact resistance, corrosion resistance, and moisture resistance.
Despite their many advantages, and there nonetheless remains a need in the art for improved ceramic materials, particularly materials having improved properties such as wear resistance. With respect to coatings, there remains a particular need for materials that demonstrate improved material toughness and strength, as well as improved bonding between the coating and the substrate coated.
The above-described drawbacks and disadvantages are alleviated by one embodiment of a microstructured or nanostructured multi-component ceramic, comprising (a) a major ceramic phase comprising a ceramic oxide composite; (b) a ceramic oxide additive; and (c) a rare earth ceramic oxide additive, wherein the total of the additives (b) and (c) comprise from about 0.1 wt % to less than 50 wt % based on the total weight of the multi-component ceramic composite. The ceramic oxide additive (b) and the rare earth ceramic oxide additive (c) may themselves comprise more than one ceramic oxide phase.
In another embodiment, a microstructured or nanostructured multi-component ceramic comprises (a) a major ceramic oxide phase comprising a ceramic oxide composite; and one of (b) a ceramic oxide additive or (c) a rare earth ceramic oxide additive, wherein the amount of the ceramic oxide additive (b) or rare earth ceramic oxide additive (c) comprise from about 0.1 weight percent to less than 50 weight percent based on the total weight the nanostructured multi-component ceramic composite.
A method for the manufacture of reconstituted, multi-component, ceramic composite powders comprises mixing and blending constituent powders, de-agglomerating the mixture of constituent powders, dispersing the de-agglomerated powders, optionally adding one or more binders to the dispersion of de-agglomerated powders, spray drying the dispersion to form reconstituted powders, and optionally heat treating the spray-dried powders.
The composites may be used as feedstocks for thermal spray of coatings, or for the manufacture of sintered, bulk ceramics. The above described and other features are exemplified by the following figures and detailed description